The present invention relates to a novel diphosphine compound, a production intermediate thereof, a transition metal complex containing the diphosphine compound as a ligand, and a transition metal complex catalyst useful as a catalyst for various asymmetric syntheses.
Hitherto, many reports have been made on transition metal complexes capable of being utilized in asymmetric syntheses such as asymmetric hydrogenation, asymmetric isomerization, and asymmetric hydrosilylation. Particularly, a complex where an optically active tertiary phosphine coordinates to a transition metal such as ruthenium, rhodium, iridium, or palladium exhibits excellent performance as a catalyst for asymmetric synthetic reactions.
In order to further enhance the performance, a large number of phosphine compounds having various structures have been hitherto developed (The Chemical Society of Japan ed., Kagaku Sosetsu (Chemical Review) 32 Yuki Kinzoku Sakutai no Kagaku (Chemistry of Organic Metal Complexes), pp. 237-238, 1982; Asymmetric Catalysts In Organic Synthesis, written by Ryoji Noyori, A Wiley-Interscience Publication). In particular, 2,2xe2x80x2-bis(diphenylphosphino)-1,1xe2x80x2-binaphthyl (hereinafter referred to as xe2x80x9cBINAPxe2x80x9d) is one of excellent optically active phosphines, and there have been already reported a rhodium complex (JP-A-55-61937) and a ruthenium complex (JP-B-4-81596 corresponding to U.S. Pat. No. 4,691,037) containing the BINAP as a ligand. Moreover, it has been also reported that a rhodium complex (JP-B-1-42959 corresponding to U.S. Pat. No. 4,604,474) and a ruthenium complex (JP-B-4-81596 corresponding to U.S. Pat. No. 4,691,037) containing 2,2xe2x80x2-bis(di-(p-tolyl)phosphino)-1,1xe2x80x2-binaphthyl (hereinafter referred to as xe2x80x9cp-TolBINAPxe2x80x9d) as a ligand affords good results in asymmetric hydrogenation and asymmetric isomerization. Furthermore, JP-B-7-68260 corresponding to U.S. Pat. No. 5,223,632 reports that a ruthenium complex of 2,2xe2x80x2-bis(di-(3,5-dialkylphenyl)phosphino)-1,1xe2x80x2-binaphthyl affords excellent results in asymmetric hydrogenation of xcex2-ketoesters.
However, since selectivity (chemical selectivity, enantio-selectivity) and catalytic activity are not always satisfactory depending on objective reaction or its reaction substrate, improvement of the catalysts are sometimes required.
It is an object of the invention to provide a novel phosphine compound and specifically, it is an object to provide a novel phosphine compound useful as a ligand for the above catalysts. Moreover, it is another object to provide a novel catalyst having an excellent performance (chemical selectivity, enantio-selectivity, catalytic activity) as a catalyst for asymmetric synthetic reactions, particularly asymmetric hydrogenation.
As a result of extensive studies for solving the above problems, the present inventors have found that a transition metal complex containing an optically active isomer of a diphosphine compound having a specific structure as a ligand is effective as a catalyst component which participates in asymmetric hydrogenation. In addition, they have found that the transition metal complex exhibits excellent catalytic activity and enantio-selectivity in asymmetric hydrogenation. Based on the findings and further investigation, they have accomplished the invention.
Thus, the present invention provides:
(i) A diphosphine compound represented by the general formula (1): 
wherein R1 and R2 each independently represents a lower alkyl group, a cycloalkyl group, an unsubstituted or substituted phenyl group, or a five-membered heteroaromatic ring residue.
(ii) A compound represented by the general formula (2): 
wherein n is an integer of 1 to 3.
(iii) A compound represented by the general formula (3): 
wherein R3 and R4 each independently represents a hydroxy group, a protected hydroxy group, a lower alkoxy group, a chlorine atom, or a bromine atom.
(iv) A transition metal complex containing an optically active compound of the compound according to (i) above and a transition metal selected from the group consisting of rhodium, ruthenium, iridium, palladium, and nickel.
(v) A catalyst containing a transition metal complex represented by the general formula (4):
MmLnXpQqxe2x80x83xe2x80x83(4) 
wherein M is a transition metal selected from rhodium, ruthenium, iridium, palladium, and nickel and L represents an optically active diphosphine compound of the compound according to (i) above; X is selected from the group consisting of Cl, Br, I, an acetoxy group, a methallyl group, and a xcfx80-allyl group; and Q is selected from the group consisting of NEt3 (wherein Et represents an ethyl group) and an dialkylammonium ion,
provided that
when M=Rh, X=Cl, Br, or I and m=2, n=2, p=2, and q=0,
when M=Ru and X=an acetoxy group, m=1, n=1, p=2 and q=0,
when M=Ru and X=a methallyl group, m=1, n=1, p=2 and q=0,
when M=Ru, X=Cl, Br, or I, and Q=NEt3, m=2, n=2, p=4, and q=1,
when M=Ru, X=Cl, Br, or I, and Q=an dialkylammonium ion, m=n=2, p=5, and q=1,
when M=Ir, X=Cl, Br, or I and m=2, n=2, p=2, and q=0,
when M=Pd and X=Cl, Br, or I, m=1, n=1, p=2, and q=0,
when M=Pd and X=a xcfx80-allyl group, m=2, n=2, p=2, and q=0, and
when M=Ni, X=Cl, Br, or I and m=1, n=1, p=2, and q=0.
(vi) A catalyst containing a transition metal complex represented by the general formula (5):
[MmLnXpZq]Yrxe2x80x83xe2x80x83(5) 
wherein M is a transition metal selected from rhodium, ruthenium, iridium, palladium, and nickel and L represents an optically active diphosphine compound of the compound according to (i) above; X is selected from the group consisting of a xcfx80-allyl group, cod, nbd, Cl, Br, and I; Z represents benzene or p-cymene; and Y is selected from the group consisting of BF4, ClO4, PF6, BPh4, Cl, Br, and I, and cod represents 1,5-cyclooctadiene, nbd represents norbornadiene, and Ph represents a phenyl group, provided that
when M=Rh, X=cod or nbd, Y=BF4, ClO4, PF6, or BPh4, and m=1, n=1, p=1, q=0, and r=1,
when M=Ru and Y=Cl, Br, or I, X=Cl, Br, or I, Z=benzene or p-cymene, and m=1, n=1, p=1, q=1, and r=1,
when M=Ru and Y=BF4, ClO4, PF6, or BPh4, m=1, n=1, p=0, q=0, and r=2,
when M=Ir, X=cod or nbd, Y=BF4, ClO4, PF6, or BPh4, and m=1, n=1, p=1, q=0, and r=1,
when M=Pd and X=a xcfx80-allyl group, Y=Cl, Br, I, BF4, ClO4, PF6, or BPh4 and m=1, n=1, p=1, q=0, and r=1,
when M=Pd and p=0, Y=BF4, ClO4, PF6, or BPh4 and m=1, n=1, q=0, and r=1, and
when M=Ni, X=Cl, Br, or I and m=1, n=1, p=2, q=0, and r=0.
(vii) A catalyst for asymmetric hydrogenation, which contains the transition metal complex according to (iv) above.
The following will explain the invention in detail.
The diphosphine compound of the invention is a compound represented by the following general formula (1): 
wherein R1 and R2 each independently represents a lower alkyl group, a cycloalkyl group, an unsubstituted or substituted phenyl group, or a five-membered heteroaromatic ring residue.
The lower alkyl group for the above R1 and R2 is an alkyl group having 1 to 5 carbon atoms, which includes a methyl group, an ethyl group, an n-propyl group, an iso-propyl group, an n-butyl group, an iso-butyl group, a sec-butyl group, a tert-butyl group, an n-pentyl group, an iso-pentyl group, and a neopentyl group. Examples of the cycloalkyl group include cyclopentyl group, cyclohexyl group, and cycloheptyl group.
The substituted phenyl group has from 1 to 5 substituents, preferably from 1 to 3 substituents. The substituent for the substituted phenyl group is preferably an alkyl group having 1 to 5 carbon atoms, an alkoxy group having 1 to 5 carbon atoms, a di(lower alkyl)amino group, or a halogen atom. The alkyl group having 1 to 5 carbon atoms herein includes a methyl group, an ethyl group, an n-propyl group, an iso-propyl group, an n-butyl group, an iso-butyl group, a sec-butyl group, a tert-butyl group, an n-pentyl group, an iso-pentyl group, and a neopentyl group. The alkoxy group having 1 to 5 carbon atoms includes a methoxy group, an ethoxy group, an n-propoxy group, an iso-propoxy group, a tert-butoxy group, and a pentyloxy group. The lower alkyl group for the di(lower alkyl)amino group is an alkyl group having 1 to 5 carbon atoms include a methyl group, an ethyl group, an n-propyl group, an iso-propyl group, an n-butyl group, an iso-butyl group, a sec-butyl group, a tert-butyl group, an n-pentyl group, an iso-pentyl group, and a neopentyl group.
The halogen atom includes a fluorine atom, a chlorine atom, a bromine atom, and iodine atom.
The five-membered heteroaromatic residue is preferably a 2-furyl group, a 3-furyl group, a 2-benzofuryl group, or a 3-benzofuryl group.
Among these compounds, a preferred compound is a compound represented by the general formula (6): 
wherein R5 and R6 each independently represents a hydrogen atom, an alkyl group having 1 to 5 carbon atoms, or an alkoxy group having 1 to 5 carbon atoms, and R7 represents a hydrogen atom, an alkyl group having 1 to 5 carbon atoms, an alkoxy group having 1 to 5 carbon atoms, or a di(lower alkyl)amino group. The lower alkyl group herein is an alkyl group having 1 to 5 carbon atoms. In this connection, the alkyl group having 1 to 5 carbon atoms and an alkoxy group having 1 to 5 carbon atoms are functional groups the same as those exemplified in the above.
Among the compounds represented by the above general formula (6), more preferred compounds are those wherein R5 and R6 are the same and are selected from a hydrogen atom, a methyl group, an ethyl group, an n-propyl group, an iso-propyl group, an n-butyl group, and a tert-butyl group and R7 is selected from a hydrogen atom, a methoxy group, an ethoxy group, an iso-propoxy group, and a tert-butoxy group.
The compound represented by the general formula (2) is also a compound belonging to the invention. 
wherein n is an integer of 1 to 3.
The compound represented by the above general formula (2) is a production intermediate for the diphosphine compounds represented by the general formulae (1) and (6).
Furthermore, the compound represented by the general formula (3) is also a compound belonging to the invention. 
wherein R3 and R4 each independently represents a hydroxy group, a protected hydroxy group, a lower alkoxy group, a chlorine atom or a bromine atom.
The protective group of the hydroxy group in the formula includes usual ether-forming groups such as benzyl, allyl, benzyloxymethyl, and a lower alkoxymethyl group. The lower alkoxymethyl group herein is an alkoxymethyl group having 1 to 5 carbon atoms and examples thereof include a methoxymethyl group, a tert-butoxymethyl group, and a methoxyethoxymethyl group. The lower alkoxy group used for R3 and R4 is an alkoxy group having 1 to 5 carbon atoms and examples thereof include a methoxy group, an ethoxy group, an iso-propoxy group, a tert-butoxy group, and a pentyloxy group.
The compound represented by the above general formula (3) is a production intermediate for the compound represented by the general formula (2).
Furthermore, racemic body, meso form, and optically active isomers of the compounds of the invention are also included in the invention.
The following will describe the process for producing these compounds.
Hereinafter, in order to avoid complication, the process for producing the compound of the invention is specifically illustrated using a compound (8) (hereinafter sometimes referred to as (xe2x88x92)-DANP) which is (xe2x88x92)-isomer of optically active isomers of the compound represented by the following formula (7) (hereinafter sometimes referred to as DANP) as an example, among the compounds of the invention. However, the process of the invention is not limited to the example. 
wherein Ph is a phenyl group.
For example, the above compound is synthesized according to the following process.
That is, 7-benzyloxy-naphthalen-2-ol (9) is dimerized in the presence of copper chloride and t-butylamine to form a compound (10), which is subjected to optical resolution using quinine to obtain an optically active isomer (R)-(xe2x88x92)-(10). The optically active isomer (R)-(xe2x88x92)-(10) is reacted with chloromethyl methyl ether (MOMCl) in the presence of diisopropylethylamine to form a compound (11), which is debenzylated in the presence of 5% palladium-carbon and ammonium formate to obtain a compound (12). Then, the compound (12) is reacted with p-xylylene dibromide in the presence of cesium carbonate to form a compound (13) and successively, the compound (13) is deprotected by adding hydrochloric acid to obtain a compound (14). The aimed compound (xe2x88x92)-DANP (8) can be produced by reacting the compound (14) with trifluoromethanesulfonic anhydride in the presence of pyridine to form a compound (15) and then reacting the compound (15) with diphenylphosphine in the presence of a palladium catalyst.
The process is shown in Scheme 1. 
wherein Bn represents a benzyl group, tBu represents a tert-butyl group, MOM represents a methoxymethyl group (xe2x80x94CH2OCH3), Tf represents a triflate group (CF3SO2xe2x80x94), Ph represents a phenyl group, dba represents dibenzylideneacetone, dppp represents 1,3-bis(diphenylphosphino)propane, iPr represents an iso-propyl group, and Et represents an ethyl group.
Moreover, (+)-isomer (referred to as (+)-DANP) of the optically active isomers of the compound represented by the above formula (7) is obtained by carrying out optical resolution of the compound (10) in the above Scheme 1 in the presence of quinidine to obtain (+)-isomer of the compound and then carrying out similar operations.
Furthermore, the compound which is a diphosphine compound described in claim 1 and wherein R1 and R2 are substituted phenyl groups can be produced utilizing a diphenylphosphine derivative having corresponding substituents instead of diphenylphosphine in the process shown in the above Scheme 1.
In addition, the compound which is a diphosphine compound described in claim 1 and wherein R1 and R2 are groups other than phenyl groups or substituted phenyl groups can be also produced in a similar manner to the process shown in the above Scheme 1, utilizing a corresponding phosphine derivative instead of diphenylphosphine.
Of the compounds of the invention, the compound (1), in particular an optically active compound thereof is useful as a ligand for a transition metal complex. Moreover, the compound (2) is useful as a production intermediate of the compound (1). Furthermore, the compound (3) is useful as a production intermediate of the compound (2).
The following will describe the transition metal complex.
As preferred transition metal complexes, the following compounds can be mentioned.
A transition metal complex represented by the general formula (4):
MmLnXpQqxe2x80x83xe2x80x83(4) 
wherein M is a transition metal selected from rhodium, ruthenium, iridium, palladium, and nickel and L represents an optically active diphosphine compound of the compound according to claim 1; X is selected from the group consisting of Cl, Br, I, an acetoxy group, a methallyl group, and a xcfx80-allyl group; and Q is selected from the group consisting of NEt3 (wherein Et represents an ethyl group) and an dialkylammonium ion, the alkyl group of the dialkylammonium ion being an alkyl group having 1 to 5 carbon atoms,
provided that
when M=Rh, X=Cl, Br, or I and m=2, n=2, p=2, and q=0,
when M=Ru and X=an acetoxy group, m=1, n=1, p=2 and q=0,
when M=Ru and X=a methallyl group, m=1, n=1, p=2 and q=0,
when M=Ru, X=Cl, Br, or I, and Q=NEt3, m=2, n=2, p=4, and q=1,
when M=Ru, X=Cl, Br, or I, and Q=an dialkylammonium ion, m=n=2, p=5, and q=1,
when M=Ir, X=Cl, Br, or I and m=2, n=2, p=2, and q=0,
when M=Pd and X=Cl, Br, or I, m=1, n=1, p=2, and q=0,
when M=Pd and X=a xcfx80-allyl group, m=2, n=2, p=2, and q=0, and
when M=Ni, X=Cl, Br, or I and m=1, n=1, p=2, and q=0.
A transition metal complex represented by the general formula (5):
[MmLnXpZq]Yrxe2x80x83xe2x80x83(5) 
wherein M is a transition metal selected from rhodium, ruthenium, iridium, palladium, and nickel and L represents an optically active diphosphine compound of the compound according to claim 1; X is selected from the group consisting of 1,5-cyclooctadiene (hereinafter referred to as cod), norbornadiene (hereinafter referred to as nbd), a xcfx80-allyl group, Cl, Br, and I; Z represents benzene or p-cymene; and Y is selected from the group consisting of BF4, ClO4, PF6, BPh4, Cl, Br, and I (Ph represents a phenyl group),
provided that
when M=Rh, X=cod or nbd, Y=BF4, ClO4, PF6, or BPh4, and m=1, n=1, p=1, q=0, and r=1,
when M=Ru and Y=Cl, Br, or I, X=Cl, Br, or I, Z=benzene or p-cymene, and m=1, n=1, p=1, q=1, and r=1,
when M=Ru and Y=BF4, ClO4, PF6, or BPh4, m=1, n=1, p=0, q=0, and r=2,
when M=Ir, X=cod or nbd, Y=BF4, ClO4, PF6, or BPh4, and m=1, n=1, p=1, q=0, and r=1,
when M=Pd and p=0, Y=BF4, ClO4, PF6, or BPh4 and m=1, n=1, q=0, and r=1,
when M=Pd and X=a xcfx80-allyl group, Y=Cl, Br, I, BF4, ClO4, PF6, or BPh4 and m=1, n=1, p=1, q=0, and r=1, and
when M=Ni, X=Cl, Br, or I and m=1, n=1, p=2, q=0, and r=0.
A transition metal which forms the complex in the invention includes rhodium, ruthenium, iridium, palladium, nickel, and the like.
These transition metal complexes can be produced using a known method.
In this connection, with regard to the symbols used in the formulae shown in the following transition metal complexes, L represents an optically active compound among the compounds (1) of the invention, cod represents 1,5-cyclooctadiene, nbd represents norbornadiene, Ph represents a phenyl group, and Ac represents an acetyl group.
The following will illustrate the complexes specifically.
Rhodium Complexes:
As a specific example of producing the rhodium complex, there may be mentioned a synthetic method wherein bis(cycloocta-1,5-diene) rhodium(I) tetrafluoroborate salt is reacted with a diphosphine compound of the invention DANP according to the method described in the Chemical Society of Japan ed., 4th edition Jikken Kagaku Koza (Lecture of Experimental Chemistry), vol. 18, Yuki Kinzoku Sakutai (Organic Metal Complexes), 1991, Maruzen, pp. 339-344. The following can be mentioned as specific examples of the rhodium complexes.
[Rh(L)Cl]2, [Rh(L)Br]2, [Rh(L)I]2,
[Rh(cod) (L) ]BF4, [Rh (cod) (L) ]ClO4, [Rh (cod) (L)]PF6,
[Rh(cod)(L)]BPh4, [Rh(nbd)(L)]BF4, [Rh(nbd)(L)]ClO4,
[Rh(nbd)(L)]PF6, [Rh(nbd)(L)]BPh4 
Ruthenium Complexes:
As the method for producing the ruthenium complex, there may be mentioned a preparative method wherein [Ru(cod)Cl2]n and a diphosphine compound of the invention DANP are heated under reflux in toluene solvent in the presence of triethylamine as described in a literature (T. Ikariya, Y. Ishii, H. Kawano, T. Arai, M. Saburi, S. Yoshikawa, and S. Akutagawa, J. Chem. Soc., Chem. Commun., 922 (1985)). Moreover, there may be also mentioned a preparative method wherein [Ru(p-cymene)I2]2 and DANP are heated under stirring in methylene chloride and ethanol according to the method described in a literature (K. Mashima, K. Kusano, T. Ohta, R. Noyori, H. Takaya, J. Chem. Soc., Chem. Commun., 1208 (1989)). The following can be mentioned as specific examples of the ruthenium complexes.
RU(OAC)2(L),
Ru2Cl4(L)2NEt3, Ru2Br4(L)2NEt3,
Ru (methallyl)2 (L),
[{RuCl(L)}2 (xcexc-Cl)3][Me2NH2], [{RuCl(L)}2(xcexc-Cl)3][Et2NH2],
[RuCl(benzene)(L)]Cl, [RuBr(benzene)(L)]Br,
[RuI(benzene)(L)]I,
[RuCl(p-cymene)(L)]Cl, [RuBr(p-cymene)(L)]Br, [RuI(p-cymene) (L)]I,
[Ru(L)](BF4)2, [Ru(L)](ClO4)2, [Ru(L)](PF6)2, [Ru(L)](BPh4)2 
Iridium Complexes:
The iridium complex can be prepared by reacting a diphosphine compound of the invention DANP with [Ir(cod) (CH3CN)2]BF4 in tetrahydrofuran according to the method described in a literature (K. Mashima, T. Akutagawa, X. Zhang, T. Taketomi, H. Kumobayashi, S. Akutagawa, J. Organomet. Chem., 1992, 428, 213). The following can be mentioned as specific examples of the iridium complexes.
[Ir(L)Cl]2, [Ir(L)Br]2, [Ir(L)I]2,
[Ir(cod)(L)]BF4, [Ir(cod)(L)]ClO4, [Ir(cod)(L)]PF6,
[Ir (cod) (L) ]BPh4,
[Ir(nbd)(L)]BF4, [Ir(nbd)(L)]ClO4, [Ir(nbd)(L)]PF6,
[Ir(nbd) (L)]BPh4 
Palladium Complexes:
The palladium complex can be prepared by reacting a diphosphine compound of the invention DANP with xcfx80-allylpalladium chloride according to the method described in a literature (Y. Uozumi and T. Hayashi, J. Am. Chem. Soc., 1991, 113, 9887). The following can be mentioned as specific examples of the palladium complexes.
PdCl2(L), PdBr2(L), PdI2(L),
[(xcfx80-allyl)Pd(L)]2,
[Pd(L)]BF4, [Pd(L)]ClO4, [Pd(L)]PF6, [Pd(L)]BPh4,
[(xcfx80-allyl)Pd(L)]Cl, [(xcfx80-allyl)Pd(L)]BF4, [(xcfx80-allyl)Pd(L)]ClO4, [(xcfx80-allyl)Pd(L)]PF4, [(xcfx80-allyl)Pd(L)]BPh4 
Nickel Complexes:
The nickel complex can be prepared by dissolving a diphosphine compound of the invention DANP and nickel chloride in a mixed solvent of 2-propanol and methanol and heating them under stirring according to the method described in the Chemical Society of Japan ed., 4th edition Jikken Kagaku Koza (Lecture of Experimental Chemistry), vol. 18, Yuki Kinzoku Sakutai (Organic Metal Complexes), 1991, Maruzen, p. 376. The following can be mentioned as specific examples of the nickel complexes.
NiCl2 (L), NiBr2 (L), NiI2 (L)
The transition metal complex containing the thus obtained novel optically active diphosphine compound as a ligand is useful as a catalyst for asymmetric hydrogenation. In the case of using the complex of the invention as the catalyst, the complex may be used after increasing its purity or the complex may be used without purification.
Among the above transition metal complexes, complexes containing ruthenium and an optically active diphosphine compound DANP as a ligand can achieve a higher enantio-selectivity as compared with ruthenium complexes of BINAP, p-TolBINAP, or the like in the asymmetric hydrogenation of dehydronaproxen.
In the case of asymmetric hydrogenation using the above transition metal complex, substrates for the asymmetric hydrogenation include carbonyl compounds, imines, olefins, and the like, specifically, xcex1-ketoesters, xcex2-ketoesters, xcex3-ketoesters, xcex1-hydroxyketones, xcex2-hydroxyketones, enamides, enol esters, allylalcohols, and xcex1,xcex2-unsaturated carboxylic acids, and more specifically, xcex1,xcex2-unsaturated carboxylic acids, preferably dehydronaproxen.
The following will describe reaction conditions in the asymmetric hydrogenation using the transition metal complex of the invention. These conditions may vary depending on a substrate and a complex to be used, but the reaction is generally carried out at a temperature of 10 to 80xc2x0 C. under a hydrogen pressure of 10 to 60 atm for 5 to 24 hours. The amount of the above complex to be used relative to the above substrate ranges from about 1/500 to 1/5000 (molar ratio). The reaction solvent to be used may be any one as far as it is stable and does not affect the substrate and product. Specifically, lower alcohols such as methanol and ethanol, ethers such as tetrahydrofuran, halogenated hydrocarbons such as methylene chloride and chlorobenzene are used. The amount thereof to be used may vary depending on the solubility of the substrate, but the solvent is used in an amount of about 0.1 to 100 volume equivalents (ml/g) relative to the weight of the substrate.
The novel diphosphine compound of the invention is particularly useful as a ligand for a transition metal complex. Moreover, the transition metal complex is useful as a catalyst for asymmetric hydrogenation. By using the catalyst, an asymmetric hydrogenation product having a high optical purity can be obtained in good yields, and thus the catalyst is industrially extremely useful.